An important consideration in the recovery of an antibiotic from aerobic or anaerobic industrial fermentation processes is the nature and properties of the micro-organism to be recovered. Non-polar antibiotics which are insoluble in water are more easily recovered by the use of a large number of water insoluble solvents such as chloroform, methylene chloride, ethyl acetate etc.; however, antibiotics such as the penicillins, tetracyclin, rifampicin, and doxorubicin, which are polar and which are present in relatively low concentrations, e.g. 0.5-5% by weight, pose a more difficult challenge. Such polar, water soluble compounds require an extraction agent of high efficiency for their recovery.
Basically the fermentation process involves inoculating a sterilized or pasteurized nutrient medium contained in a fermentor with between about 1 wt % and about 10 wt % of a culture of the desired microorganism, or its enzyme usually in the logarithmic phase of its life cycle. The temperature and pH of the fermentation broth is closely controlled during catabolism to between about 20.degree. and 40.degree. C. and 6 to 8 pH. After a period of from about 3 days to about 3 weeks the desired antibiotic is produced. Antibiotics, thus produced include macrolides, polyenes, polypeptides, penicillins, tetracyclines, and the like. The desired fermentation product contained in the broth, together with nutrients, such as sugars, alcohols and salts as well as original and often mutant microorganism forms, then enters the product recovery stage. Heretofore, recovery has been accomplished by a series of time consuming chemical and physical treatments which include chilling, heating, distillation, extraction, evaporation, crystallization, solubilization and recrystallization in order to isolate a substantially pure antibiotic useful in human and animal therapy. It is evident that the recovery is considerably more costly than the preceding fermentation and improved methods for product recovery have long been saught for process economy and commercialization.
Accordingly, it is an object of this invention to provide an improved and commercially feasible process for the recovery of water soluble, and other polar antibiotics from aqueous fermentation broths and to supply an extractant composition suitable for isolating said antibiotic products from a fermentation broth.
Another object is to provide a select group of chemical compounds which have the unique property of extracting desired antibiotics.
These and other objects of the invention will become apparent from the following description and disclosure.
In accordance with the present invention, there is provided a group of water insoluble or partially water soluble lactams for antibiotic extraction having the formula ##STR1## wherein n is an integer having a value of from 1 to 3 and R is alkyl having from 8 to 14 carbon atoms. These extraction agents have the unique capability of extracting 90% or more of the polar, antibiotics of this invention from a fermentation broth.
The chain length of the R group attached to heterocyclic nitrogen is critical to the operation of the present invention since alkyl groups below C.sub.8 are water soluble and thus prevent phase separation of the product contained in the fermentation broth, an essential feature of the present invention. Alkyl groups above C.sub.14 are solid and cannot be utilized for extraction.
Of the above extraction agents, those having a relatively low critical micelle concentration of between about 1.times.10.sup.-3 and 1.times.10.sup.-4 mole per liter of water, and wherein R is C.sub.8 -C.sub.12 alkyl and n is one, are preferred. Most preferred for extraction of water soluble antibiotics in N-octyl-2-pyrrolidone.
The extraction agent of this invention can be any of the above described lactams employed individually or in admixtures to suit the purposes of a specific operation. Also, the lactam extractant can be used in an undiluted state or in solution with a water insoluble solent, such as butyl acetate, ethyl acetate, n-butanol, toluene, methylene chloride, chloroform, and the like, when added to the fermentation broth. When solutions of the lactams are employed, concentrations as low as 2 wt % of lactam in solvent can be employed; however, from the standpoint of economics and concentration control, it is preferred to employ the present lactam extractants in an undiluted state.
The microorganisms of this invention which undergo aerobic and anaerobic fermentation to provide valuable polar, products containing a phenolic and/or carboxylic group include animal forms such as slime molds, protozoa, bacteria, fungi, lichens and algae.
The following Table I provides some specific examples of microorganisms used in the preparation of the present products.
TABLE I ______________________________________ Antibiotic Producer Organism Compound Chemical Type ______________________________________ Penicillium Chrysogenum Penicillin V .beta.-Lactam Penicillium Chrysogenum Penicillin G .beta.-Lactam Cephalosporium acremonium Cephalosporin C .beta.-Lactam Streptomyces peuceticus Doxorubicin Anthracycline var. caesius Streptomyces peuceticus, S. Daunorubicin Anthracycline coeruleorubidus Streptomyces nodosus Amphotericin B Polyene Streptomyces griseus Streptomycin Aminoglycoside Streptomyces aureofaciens Tetracyclins Polypeptide Streptomyces orientalis Vancomycin Glycopeptide Streptomyces lasaliensin Lasalocid Polyether Nocardia mediterranei Rifamicins Ansamycin ______________________________________
Of the above types, the microorganisms streptomyces, penicillium, cephalosposium, and norcardia which produce commercially valuable products are preferred.
Generally the process of this invention is carried out at a temperature of between about 20.degree. C. and about 50.degree. C. under a pressure of from about 14 to about 50 psig, preferably at a temperature between about 25.degree. and 35.degree. C. and ambient pressure. The process involves filtration of the fermentation broth to remove water insoluble materials such as mycelium, and adding between about 0.2% and about 10% by weight of the present extraction to the filtrate. Preferably, when the lactam of the present invention is the sole extractant in the process, between about 1% and about 5% by weight is added to the broth. However, it is within the scope of this invention to employ the present lactam as a supplementary extractant to a conventional extraction agent which may be used in the system. In the later case as little as 0.2 wt% of the present lactam can be used to provide greatly improved results. In either case, the total amount of extractant introduced into the recovery process should be between about 1% and about 10% by weight, preferably between about 1.5% and about 5% by weight, with respect to the fermentation broth. Generally the weight ratio of extractant to product is maintained between about 500:1 and about 10:1, preferably between about 100:1 and about 20:1.
In the case of water soluble products, after uniform incorporation of the extractant, the broth separates into an organic phase and an aqueous phase. The organic phase containing the desired antibiotic can be recovered in at least 90% purity in a single separation step. The extractant with desired product can be utilized as the product of the process, or the organic phase can be subjected to further treatment for removal and recovery of lactam.
Alternatively, the lactam extractant can be removed from the antibiotic by chromatography using normal phase or reverse phase silica gel chromatography, gel filtration counter-current distribution, high pressure liquid chromatography etc. using a wide variety of solvents or solvent mixtures, namely hexane, toluene, methylene chloride, chloroform, ethyl acetate or butyl acetate. The lactam can then be recycled to the extraction zone in the system. This lactam recovery and recycled operation provides for an economical and continuous process.
The principles of the present invention can be applied to fermentations of a wide variety of polar materials. Thus the products which can be extracted by the present process include any of the polar, water soluble or water insoluble antibiotics, organic acids, vitamines, nucleosides, peptides, nucleotides, amino acids and miscellaneous products listed on pages 865-868, Volume 9 of Kirk Othmer's Encyclopedia of Chemical Technology, 5th Edition. Preferred of these are the antibiotics containing a phenolic and/or carboxylic group such as penicillins, cephalosporins, anthracyclins, rifampicins, vancomycins, tetracyclins etc.
A major advantage of the above process is that the present lactams can be used to recover 90% or more of a water soluble product from a product lean broth without resorting to distillation and subsequent evaporation and crystallization steps. Thus, the present process materially reduces the process time and cost of conventional recovery processes now in use.
Having thus described the invention, reference is now had to the following examples which illustrate preferred embodiments but which are not to be construed as limiting to the scope of the invention as more broadly defined above and in the appended claims.